Field of the Invention
This invention relates, in general, to the production of fluids from a hydrocarbon producing well. In particular, this invention relates to efforts to provide systems for the gathering of natural gas which use the space in and around the well site as efficiently as possible.
Description of the Related Art
Fluids are produced from hydrocarbon producing formations under the Earth's surface. An example of a hydrocarbon producing formation is a coal seam. Coalbed Methane (CBM) is produced by drilling a well into a coal formation and collecting the entrapped methane gas located within the formation. While entrapped in the formation, the methane gas is under pressure. The gas naturally migrates to the low pressure area created by the well. Liquids such as water similarly migrate to this low pressure area.
Liquid Removal
The accumulated liquid must be removed so that gas can continue to flow from the well. In a typical pumping arrangement, the liquid is drawn to the surface through tubing running from a down-hole pump located at the bottom of the well to the surface. Gas flows from the well through the annulus, the space between the well and the tubing. Once brought to the surface, the liquid must be removed from the well site. Currently, two methods are used to remove the liquid.
Liquid Removal by Truck
One method of gathering and disposing of the liquid is to pump fluids directly from the well into localized tanks or other holding facilities. Trucks then travel to and from the collection tank to dispose of the liquid. However, this method requires a great deal of man power, reliable roads, and expensive road maintenance. The weight and amount of travel from the trucks damages roads to well sites as well as any community roads which the trucks must travel on during the trip to the collection facility. Local communities often require gas producer to pay for maintenance of the community roads. The expense and liability of on-road fluid gathering and distribution can be costly and potentially unpopular within the community. In the winter snow and ice can create adverse road conditions that make it difficult for trucks to travel to and from the well site.
Liquid Removal by Pipeline
A second method of removing liquid is to install a pipeline for the liquid to enter as it exits the well. The pipeline could run from the well site to a collection facility. Conventionally, the pump-jack and/or down-hole pump is the mechanism used to push the liquid through the pipeline because it has positive displacement capabilities far beyond what is necessary to simply bring fluids to the surface. The excess pressure capability can be utilized as the mechanism to push liquid through a pipeline network to the central collection facility. However, a disadvantage of using the pump-jack to force liquid through a pipeline is that the pump-jack will cause a pressure surge or water hammer to move through the pipeline. Therefore, a larger diameter pipeline is required to accommodate these short duration surges, than would be required if the same total volume of liquid moved through the pipeline at a substantially constant flow rate.
Problems Caused by Gas/Liquid Mixtures
Fluid, brought to the surface by a well, typically contains a liquid component and a gas component. The presence of the gas component raises additional problems which are not fully addressed by conventional methods of gas and liquid separation and removal. When the fluid is pumped directly to the pipeline without conventional gas and liquid separation, any gas entrained in the liquid is typically lost. This problem is further compounded by a condition know as over-pumping. Over-pumping occurs when the pump operates more than is necessary to remove the liquid from the well. Once the liquid is removed from the well and the pump continues to run, natural gas is allowed to escape from the wellbore and is pumped into the tubing and into the liquid pipeline. The presence of gas in the liquid pipeline also makes it difficult to accurately measure the volume of liquid which is removed from the well because currently used methods for measuring flow through a pipeline cannot distinguish between gas flow and liquid flow.
When gas is introduced into a liquid pipeline the possibility of an air-locking condition is created. Air-locking occurs when gas gathers in the highest elevations in the pipeline and causes a complete or partial blockage of liquid flow. The gathering of gas can be from gas that separates from the fluid mixture or from gas that is introduced when the well is over-pumped. When air-locking occurs the liquid cannot be pushed past the gas blockage. As the pump continues to try to force liquid past the air-lock blockage, the pressure in the portion of the pipe before the blockage continues to increase. When the pressure reaches a pressure beyond the maximum rating of the pipeline, a rupture can occur. Pipeline ruptures can be difficult to diagnose and locate. Furthermore, ruptures can be expensive both in terms of costs associated with repairing damaged equipment and in cleaning up environmental damages from liquid which leaks from the ruptured pipeline.
In addition to the risk of pipeline rupture, the pump-jack also creates pressure on the wellhead itself and the packing surrounding the wellhead. The pump-jack is typically connected to the down-hole pump by steel rods that extend from the entire depth of the well. The rod connected to the pump-jack at the surface is known as the polish rod because of its smooth and polished surface. A packing material at the wellhead allows the polish rod to move up and down in the well while containing the pressure of the water in the tubing. This packing must be monitored frequently because it often leaks unexpectedly and has to be replaced on a frequent basis. In fact, spillage associated with packing leakage is difficult if not impossible to eliminate.
Cold Weather
Another problem associated with current methods of storing, removing, and transporting liquid such as water from a well site is the danger that the liquid will freeze during cold weather. The frozen water can limit well production and also rupture pipelines and promote wellhead spillage.
Installation and Servicing Concerns
Finally, current methods of setting up a pumping assembly at a well site take two to three days before the site is ready to begin pumping fluid from the well. Under the current method of installing a pumping assembly, the pump is assembled in a piecemeal fashion at the well site. As a result, even pumping assemblies located close together often are not constructed according to a uniform plan and do not use the same components. The piecemeal method of installation takes a long time to complete and makes maintenance and repair difficult. Furthermore, space within the pumping assembly is not utilized as efficiently as possible. As a result, the footprint of the installed pumping assembly is larger than is necessary to accomplish all functions of the assembly. Similarly, as a result of the lack of uniformity in gas well construction and large footprint area, gas wells generally do not have a uniform aesthetically pleasing appearance.
In addition to difficulties created by current installation practices, further difficulties arise because gas producing wells must be serviced regularly. To service the down-hole pump and other elements located within the well, a large truck hauling a gin pole and pulley system must drive up to the well site. The pulley system is used to hoist the down-hole portions of the pumping assembly from the well. The problems associated with building and maintaining access roads to the well site, described above for liquid transportation trucks, applies similarly to these service trucks which also must access the well site regularly.
For the reasons stated above, there is a need for a method and apparatus for removing liquid from a well site which can accomplish liquid removal without the use of hauling trucks or large diameter pipelines. Furthermore, the apparatus and method should prevent complications that lead to air-locking and pipeline ruptures. The method and apparatus should also address the problem of pipeline freezing so that it can be used in cold weather. Finally, there is a need for a method and apparatus for liquid removal which makes more efficient use of space in and around the wellhead and which can be installed more quickly so that pumping can begin in a more timely fashion. Furthermore, the gas well should have a uniform aesthetically pleasing appearance.